One who can not sleep typically harbors a busy mind or a guilty conscience or a combo of the two. Those who are innocent are able to slumber peacefully. Macbeth has murdered sleep for himself and also for his wife (who later sleepwalks as a result of her guilt) because he takes the innocent life of Duncan who trusts Macbeth both as his loyal countryman and as his host. Macbeth has broken many rules by taking Duncan's life, and he will never be able to sleep peacefully again as a result of it: "'Sleep no more!/Macbeth does murder sleep'...."
By killing Duncan in his sleep, Macbeth has brought tremendous guilt on himself and imagines he hears a voice saying "Macbeth has murdered sleep!" He feels he will never sleep again because he destroyed the slumber (and life) of Duncan. Ironically enough, his wife's sleep is also destroyed by guilt as we see later when she is sleep walking.
Methought I heard a voice cry 'Sleep no more!
Macbeth does murder sleep', the innocent sleep,
Sleep that knits up the ravell'd sleeve of care,
The death of each day's life, sore labour's bath,
Balm of hurt minds,... (2.2)